Thanks to high efficiency, ranging from 100 to 150 lm/W, high intensity discharge lamps are widely used in urban and large-format lighting systems. In typical ignition and supply systems of high intensity discharge lamps, there are an inductive ballast (BALLAST) and a starter, which generates a high voltage on this ballast until a moment of lamp ignition. After an ignition, ballast's inductance limits a flow of current through a lamp. In order to reduce degradation of electrodes, a square wave supply voltage is most often used for supplying high intensity discharge lamps with limiting inductance (BALLAST).
A typical system for supplying discharge lamps from AC mains is composed of a diode rectifier and a power factor correction system (PFC), which are an internal source of stabilized voltage of about 400V. This voltage supplies a cascade system of electronic switches (transistors), FULL or HALF BRIDGE types, which being controlled by a proper control system is a source of alternating voltage of set value, at which the value of serial inductance limits the current running through a lamp to the set value. Circuits with regulated frequency are complemented a condenser being parallel to a lamp and serial to an inductance, to obtain a serial resonant circuit. Generating an alternating voltage of a frequency close to self resonant frequency of this circuit in the switches cascade induces a high alternate voltage in a condenser of said circuit. This voltage is used to initiate an ignition of discharge lamps.
The document “High Intensity Discharge lamps—Technical information on reducing the wattage”, published by the OSRAM company in February 2009, discusses methods of reducing and regulating of a power supplied to discharge lamps. In typical solutions, the only element stabilizing a power supplied to a lamp is an inductance whereas a power regulation, at set current stability and mains frequency, is done by selecting an inductance for predicted power. Such solution is sensitive to changes of mains parameters and in practice, it forces constructing a separate supply network for urban lighting systems.
Supplying high intensity discharge lamps using frequencies over 1 kHz causes forming of acoustic waves, which in a wide frequency range of supply courses (from 1 kHz to 1 MHz) result in an appearance of acoustic resonance. This phenomenon destabilizes a flow of current through plasma causing an instability of discharging arc, lamp blinking and in extreme cases even mechanical damage of a burner. Typical methods of eliminating this effect consist in supplying high intensity lamps with voltages of two courses—the main one of a frequency range in which the resonance can occur, and the second one of higher frequency which stabilizes the discharging arc. European patent specification EP 1327382 discloses the method of supplying discharge lamp, in which in order to reduce an adverse acoustic resonance, a frequency modulation (FM) and pulse width modulation (PWM) of square-wave voltage supplying the ballast are used, what results in an additional amplitude modulation (AM) of supplying wave.